Details of what specific structures are in the footage are explained by BBC:

Auschwitz was the largest camp established by the Germans during World War II. More than a million people – the vast majority of them Jews – died there between 1940, when it was built, and 1945, when it was liberated by the Soviet army.

Railway tracks into Auschwitz-Birkenau – Trains filled with victims from throughout occupied Europe arrived at the camp almost every day between 1942 and the summer of 1944.

Ruins of wooden huts at Birkenau – Birkenau (or Auschwitz II) was erected in 1941 solely as a death camp, the wooden huts are now in ruins with only brick fireplaces and chimneys remaining.

Auschwitz I – The brick-built buildings were the former cavalry barracks of the Polish Army.
Courtyard between blocks 10 and 11 at Auschwitz I – Block 11 was called “the Block of Death” by prisoners. Executions took place between Block 10 and Block 11 and posts in the yard were used to string up prisoners by their wrists.